Processing of magnetic materials



July 18, 1967 G. Y. CHIN ETAL PROCESSING OF MAGNETIC MATERIALS Filed May14, 1964 CURRENT SOURCE WRITE-RAD r m R IN LO Q 5mm wmw m r 65 C W M a mum m w m z A. 2). l s 2 w a 2 y. x a a a u V-COORD/NA TE WRITE CURRENTPULSE CIRCUITS INF ORMA T/ON U T/ L IZA T/ON C/RCU/TS 6. K CHININVENTORS J H WERN/CK A T TORNE l United States Patent l York Filed May14, 1964, Ser. No. 367,321 Claims. (Cl. 148-120) This invention isdirected to a method for the manufacture of magnetic alloys. Ofparticular interest is the fabrication of soft magnetic materials in theform of thin tapes which are then useful for the manufacture of variousmagnetic devices. One such device, a memory structure known as atwistor, is described in claimed in United States Patent No. 3,083,353issued March 26, 1963.

A modification of this device of particular current interester which mayutilize this invention in the piggyback twistor described and claimed inUnited States Patent No. 3,067,408 issued December 4, 1962.

The aforementioned devices are designed for use in memory arrays forstoring binary information in temporary or permanent form. Theinformation is stored in a segment of a helical flux path provided alonga magnetic conductor. A transverse write-read conductor is inductivelycoupled to the helical flux path. This invention is directed to thefabrication of a magnetic material useful in the device of FIG. 4 ofUnited States Patent No. 3,083,353 in which the helical flux path is adiscrete wire or ribbon wrapped around an electric conductor. It is alsoapplicable to the devices described in United States Patent No.3,067,408 issued December 4, 1962. Other uses will become apparent.

The magnetic materials which have been preferred for devices of theaforementioned character are nickel-iron alloys having 40 to 90 percentnickel. Particularly useful is molybdenum Permalloy which contains 4percent molybdenum and 79 percent nickel. Certain other minor additionssuch as manganese and silicon are often added to improve themetallurgical processing ofthe alloy.

The conventional manner of preparing magnetic tapes of these alloys isto cast the alloy into an ingot. The ingot is then hot-worked to abillet having a cross-section of the order of 0.1 in. or less andthereafter subjected to a series of cold working operations withintermediate anneals until the desired tape or wire size is obtained.The casting, generally of the order of several square inches in section,cannot be cold-worked to the desired size due to the brittleness of thealloy. Once the billet is reduced to a size of 0.1 in. the alloy canthen be completely cold-worked in any desired manner. These cold workingoperations are also known to enhance the magnetic characteristics of thematerial. This processing technique is described in United States PatentNo. 2,783,170. In accordance with the present invention a uniformcrystal texture and composition are established within the material byinitially zone melting the alloy.

The float zone melted rod is then cold worked with or withoutintermediate anneals to obtain the desired wire or tape.

The advantage of producing magnetic tape in this manner is in theextreme uniformity of the magnetic properties of the processedmaterials. Using the prior art technique tape produced from one ingotmay be well within the desired specification while for reasonspreviously unknown the successive batch is commercially worthless. Largedeviations from one tape length to another within the same batch havebeen found. The reasons for these inconsistencies are now understood andare attributable to compositional inhomogeneities and non-uniformcrystal texture. Both of these variables are eliminated accordingPatented July 18, 1967 to the present technique with the result that theultimate magnetic properties of the tape are thoroughly predictable andreproducible.

The hysteresis characteristics of the nickel-iron alloys to which thisinvention is directed are related to the orientation of nickel-nickeland iron-iron atom pairs. The direction of orientation of theselike-atom pairs results in a hard magnetic direction so it becomesdesirable to align as many pairs as possible in a single crystaldirection or plane thus producing a large magnetic anisotropy and aneasy magnetic axis in the normal direction.

A nickel-iron crystal such as Ni Fe possesses a facecentered cubicstructure which in the ordered crystal state prefers to have alternatenickel-iron atoms. The desired magnesic anisotropy results from pairingiron atoms and nickel atoms. This is usually achieved by mechanicallyforcing a realignment of the atoms along slip planes so that pairsresult. Since the crystal prefers to slip along a {111} crystal plane ina ll0 direction the pairs will form in a direction normal to the slipdirection. In the case of a single crystal elongated in the [111]direction the pairs will tend to align in the ll0 directions lying onthe (111) plane thereby making the [111] direction an axis of easymagnetization.

The prior art procedures for fabricating tape such as that described inUnited States Patent No. 3,086,280 ignore the original crystal textureof the cast alloy. However, they often produce a successful productsince, in the process of Working the wire by drawing in a single axialdirection, the Wire tends to develop a 11l texture in the direction offlow and the magnetic anisotropy resulting from the mechanically inducedpairings produces a significant 11l easy axis. However, the amount ofll1 texture originally present and the texture developed in the wireduring cold drawing is not wholly controllable and variations areoccasionally found from one batch to another. The magnetic squareness ofthese sections is understandably different.

According to this invention the importance of this crystal texture isnow realized and the wire is initially given a completely uniform l1ltexture prior to working it to the desired form. It has been found thatthis texture is preserved throughout the process of drawing the wire andall wire made according to a given set of cold working and annealconditions will exhibit'consisteutly uniform magnetic characteristics.

In the process of roll flattening the 111 textured wire to form tape thealloy is made to flow in a direction normal to the wire axis. In sodoing the tape is found to have a 21l orientation in the flow directionwhile maintaining the ll1 direction along the wire axis. The like-atompairs induce-d along slip planes in the laterally deformed material arefound to lie close to the 1l1 tape axis and thus some of the magenticanisotropy present in the wire prior to roll flattening is destroyed.

Consequently if roll flattening is to be used it is found desirable toanneal the wire prior to the flattening step. The result of this annealis to introduce some cubic texture into the wire axis prior to rollflattening. When this wire is now made to flow laterally the slip planesdue to the 100 texture component are arranged so that like-atom pairsoccur in the desired plane, that is, normal to the tape axis.Consequently even though roll flattening is harmful to a tape with l11texture in terms of squareness, the presence and behavior of a 100component in the wire compensates for the loss in squareness which wouldbe expected if the wire texture was pure 1l1 The anneal is eflective inproducing a cubic texture because the cubic crystal habit is preferredby the wire on recrystallizing. The details of this intermediate annealare described and claimed in United States Patent No. 3,086,280. Theanneal conditions prior to roll flattening have been determined asfollows. The cold-drawn wire is heat treated at a temperature in therange of from 100 C. to 900 C. for one second to 24 hours, the shortertimes corresponding with the higher temperatures. The temperatures andtimes of the heat treatment are interrelated so as to require a minimumtemperature of one second and a maximum time of four seconds for thetemperature range of 700 C. to 900 C. and a heat treatment of 24 hoursat 100 C.

This heat treatment produces the desired amount of cubic texture in thewire and the wire is then ready to roll-flatten to the appropriatedimension.

Whereas roll flattening is the procedure commonlyemployed for makingmagnetic tape, it is now found that if I the wire is die-drawn into thedesired ultimate shape, the

foregoing heat treatment becomes unnecessary. This is because the wireis deformed axially in die-drawing and 7 there is no significant lateralflow of the wire as in the.

case of roll flattening. Hence a pure 111 texture is desirable.

In processing a zone refined single crystal of the alloy it is notnecessary to make additions of silicon or manganese to facilitatemechanical working. Thus the elimination of these and other contaminantsfrom the magnetic composition contributes to the ultimate uniformity andpredictability of the magnetic characteristics of the material.Furthermore the discovery that an alloy produced by zone melting can becompletely cold-worked thus eliminating the hot working operation andattendant oxidation'of the alloy is a significant technical advance.

Exemplary device applications for which the material .of this inventionis adapted are treated in the following description. In the drawing:

FIG. 1 is a perspective view of a magnetic memory element utilizing thematerial made by the process of this invention; and

FIG. 2 is a schematic representation of a magnetic matrix illustratingthe practical utilization of the element of FIG. 1 for informationstorage and retrieval.

While the magnetic tapes or wires produced in accordance with thisinvention may find a variety of uses this description is made in termsof one exemplary device application, the twistor. The term twistor wasapplied to devices of this type since the device as originally proposedpossessed a helical flux path made by mechanically twisting theconductor. However, this flux patterncan also be obtained by Wrapping anelectrical conductor with a helix of magnetic wire or tape and it isthis form of the device which now appears to be preferred'due to theobvious difiiculties in applying and maintaining a uniform mechanicalstress on wires of very small dimensions.

The tape-wrapped twistor is shown in FIG. 1. The rod 10 is an electricalconductor such as a copper wire having a helically wound tape 11 wrappedat a 45 angle with the wire axis. The tape 11 consists of a magneticalloy such as Permalloy fabricated in accordance with this invention.One end of the conductor 10 is connected to ground and the other end isconnected to a write-read current source 12. Since devices of thischaracter usually relyon coincident write and/or read on orthogonalcoordinates defining the address, a coil 13 is inductively coupled tothe conductor .10 to establish a field normal to that of the conductor.The coil 13 is connected to ground and to a suitable write-read currentsource 14. In practice the coil 13 is generally a single conductorinductively coupled to the conductor 10 as seen in FIG. 2.

. The current sources 12 and 14 may be of any known type and are shownin block form for convenience.

In the operation of the device the information stored is read bydetermining the remanent magnetization of a portion of the wire at theaddress of interest. The binary information is written by coincidentcurrent pulses fed to the address along the coordinate conductors 10 and13. The state of magnetization at the address is represented by eitherof the directions indicated by the arrows, and is indicated by thepresence or absence of a pulse generated by a switching field applied ina predetermined direction.

Assuming the presence in the tape 11 of a flux in one direction asrepresented by the arrows, a current must be applied of a magnitudesufficient to generate a magnetomotive force which will switch thedirection of flux in the opposite direction of the helical path. Themagnitude of this force may be determined as h. When a current pulseproducing a magnetomotive force of the magnitude h/ 2 is now appliedfrom the source of a polarity to oppose the helical flux simultaneouslywith a current pulse producing a magnetomotive force of the magnitude h/2 from the source, the total magnetomotive force will be suflicient toswitch the flux state of the tape 11. The polarity of the current pulserequired from the source will depend upon the sense of the winding ofthe solenoid 13. The flux state to which the tape 11 has been thusswitched may be regarded as a particular information bit, say a binary1, which it is desired to store and this operation would constitute thewrite phase of the memory function. It should be noted that, inaccordance with the principles of coincident current memory elementsgenerally, either of the current pulses applied from the sources 12 and14 alone will be insufficient to accomplish the magnetic switching.

Information stored in the tape 11 is read outby reversing the polarityof the currents applied from the current sources. The simultaneousreverse current pulses will again cause a switch in the direction ofmagnetization in the helical path if an information bit has been pre-'viously stored in the manner described above. Obviously, if in the writephase of operation the tape 11 had not been magnetically switched forwhatever reason, no switching will occur during the read-out phase. Whenthe magnetic state of the tape 11 is switched, a change in the potentialbetween its ends will result. This change may be detected by suitabledetection means 15 as an output pulse superimposed upon the switchingcurrent pulse applied to the conductor 10. When the magnetic state ofthe tape 11 is not reversed with respect to polarity, as would be thecase, say if a binary 0 had been stored, no pulse will be read.

Read-out may also be'accornplished by' simply overdriving the solenoid13 by a current producing a sufficient reverse magnetomotive forceapplied from the current source 14 alone. In this case the conductor 10would act only as a read-out lead, the output signal also being detectedby the means 15. This meansof read-out is particularly adaptable in theemployment of the memory element of this invention in the formation ofmemory arrays as will be described with respect to FIG. 2. 7

In FIG. 2 a coordinate memory array is illustrated. Such an arraycomprises a lattice of transverse parallel conductors 20 wrapped withmagnetic tape 21 and parallel conventional insulated copper conductorsconstituting the solenoids 22. One end of each of the conductors 20 and22 is connected to a ground bus 23. The other end of each of thesolenoids 22 is connected to suitable-y coordinate write current pulsecircuits 24. Such circuits are well known in the magnetic memory andinformation handling art and in this case would produce appropriatelytimed The other end of each of the conventional conductors 20 isconnected to suitable x coordinate write and read current pulse circuits26 also well known in the art and similar in operation to the Writepulse circuits included in the block 24. The illustrative memory arrayof FIG. 2

is word-organized, that is, the information bits of each word storedappear at the portions of the solenoids 22 inductively coupled to thetransverse conductors 20. In the Writing operation in the array the wordlevel is selected by applying a current pulse of the proper magnitude toa selected x coordinate conductor 20. Simultaneously the particular bitinformation is introduced by pulsing the y coordinate conductors 22inaccordance with the bits of the word to be stored. The read operation issimply performed by applying a read current pulse of opposite polarityto that of the write current pulse and of proper magnitude to only theparticular x coordinate conductor 20 defining the row in which the wordappears. Output signals will then appear in parallel form at theterminals of the conductors 22 which contained the information bits ofthe word read out.

The magnetic tape or wire used in the device described is prepared byzone melting the required amounts of high purity nickel and iron andother ingredients such as molybdenum where required. The zone meltingtechnique and suitable apparatus are described in B. F. Oliver, Trans.AIME, vol. 227, p. 960, 1963.

The details of the zone refining procedure may vary according toaccepted prior art practice. See Zone Melting by W. G. Pfann, John Wiley& Sons, Inc., 1958. No invention is predicated on zone melting the alloyper se.

The following procedure is given by Way of example:

The proper amounts of high purity Ni, Fe and Mo (4 wt. percent Mo, 70Wt. percent Ni, 17 Wt. percent Fe) powders are mixed together thoroughlyand pressed into bars. These pressed bars have sufficient mechanicalstrength that they can be zone refined Without presintering.Alternatively, rods of Mo, Ni, and Fe of the proper diameters to givethe above composition can be bundled together. One forward pass and onereverse pass result in a chemically uniform material. The molten zonetravel rate used is 0.0015/sec. However, faster rates can be employed.

The rod or billet which is to be cold worked is initially given a pure111 crystal orientation in the direction the rod is to be cold worked.Accordingly a properly oriented seed crystal is employed to give the 111crystal orientation in the axial direction of the rod.

Various other modifications and extensions of this invention will becomeapparent to those skilled in the art. All such variations and deviationswhich basically rely on the teachings through which this invention hasadvanced the art are properly considered within the spirit and scope ofthis invention.

What is claimed is:

1. A method for processing magnetic alloys composed substantially ofnickel and iron to produce magnetic wire or tape which comprises thesteps of zone melting the magnetic alloy to form a single crystal bodyand colddrawing the single crystal body in a l11 crystal direction toproduce the ultimate desired product.

2. The method of claim 1 applied to an alloy composition ofapproximately 4 percent molybdenum, 79 percent nickel, balanceessentially iron.

3. A method for processing magnetic alloys composed substantially ofiron and nickel to produce magnetic wire or tape which comprises thesuccessive steps of zone melting a body of the magnetic alloy to form asingle crystal, cold-drawing the single crystal in essentially a l1lcrystal direction to form a wire, heat treating the colddrawn wire at atemperature in the range of from C. to about 900 C. for one second to 24hours, the shorter times corresponding with the higher temperatures, thetemperatures and times of the heat treatment being so interrelated as torequire a minimum time of one second and a maximum time of four secondsfor the temperature range of 700 C. to 900 C. and a period of 24 hoursat 100 C., further cold-working said wire so as to reduce its diameter aminimum of five percent, and flattening the cold-drawn wire to form atape of the desired dimensions.

4. The method of claim 3 applied to a magnetic alloy composed of 4percent molybdenum, 79 percent nickel, balance essentially iron.

5. The method of claim 3 wherein the heat treatment is conducted at atemperature of approximately 800 C. for a period of approximately onesecond.

References Cited UNITED STATES PATENTS 1,560,335 11/1925 Czochralskil48l.6 1,586,887 6/1926 Elmen 148100 2,124,607 7/1938 Buchner et a1.l48l01 2,940,882 6/1960 Hibbard et al. 148-l01 2,943,007 6/1960 Walteret al. l48-120 3,086,280 4/1963 Gibbs et a1. 148-120 3,164,496 l/l965Hibbard et a1 148-420 FOREIGN PATENTS 1,275,991 10/1961 France.

DAVID L. RECK, Primary Examiner.

HYLAND BIZOT, Examiner.

N. F. MARKVA, Assistant Examiner.

3. A METHOD FOR PROCESSING MAGNETIC ALLOYS COMPOSED SUBSTANTIALLY OFIRON AND NICKEL TO PRODUCE MAGNETIC WIRE OR TAPE WHICH COMPRISES THESUCCESSIVE STEPS OF ZONE MELTING A BODY OF THE MAGNETIC ALLOY TO FORM ASINGLE CRYSTAL, COLD-DRAWING THE SINGLE CRYSTAL IN ESSENTIALLY A <111>CRYSTAL DIRECTION TO FORM A WIRE, HEAT TREATING THE COLDDRAWN WIRE AT ATEMPERATURE IN THE RANGE OF FROM 100*C. TO ABOUT 900*C. FOR ONE SECONDTO 24 HOURS, THE SHORTER TIMES CORRESPONDING WITH THE HIGHERTEMPERATURES, THE TEMPERATURES AND TIMES OF THE HEAT TREATMENT BEING SOINTERRELATED AS TO REQUIRE A MINIMUM TIME OF ONE SECOND AND A MAXIMUMTIME OF FOUR SECONDS FOR THE TEMPERATURE RANGE OF 700*C. TO 900*C. AND APERIOD OF 24 HOURS AT 100*C., FURTHER COLD-WORKING SAID WIRE SO AS TOREDUCE ITS DIAMETER A MINIMUM OF FIVE PERCENT, AND FLATTENING THECOLD-DRAWN WIRE TO FORM A TAPE OF THE DESIRED DIMENSIONS.